Unbreaking the camel’s back
Darwin Medal Lecture: Terry Hughes
OK, so after an involuntarily induced solar radiation based hiatus (sunstroke) break, I’m back. And just in time – it’s the Darwin Medal lecture by the latest recipient, Terry Hughes. I’ll blog it before my kidneys pack in.
As you’ll know, Charles Darwin wasn’t just a bit cluey about how species form. He also knew a thing or two about geology, and brought the two disciplines together in his brilliant work on coral reefs. So this medal is a Big Deal.
Terry gets his gong. Then goes into his thank you speech. It’s just like the Oscars, only shorter and without the tears. Thanks for your consideration Terry.
He seems a little nervous, having counted the number of seats in the Grand Floridian Ballroom. Over two thousand. Wonder whether he counted a sample then scaled up, or whether he counted each and every one…
He’s going to talk about the concept of reef resilience, then the Caribbean Diadema die-off, which he reckons only “old farts” like him remember. Then he’ll wrap up with a bit about reef governance.
Resilience is the “ability of a system to absorb insults or disturbances without flipping into a fundamentally different state”. So, like loads of sub-tropical sunshine either does or doesn’t cause one to spend the next day with a splitting headache and inability to stand up.
Now for the science. Reefs can be either coral dominated or something-else dominated (like algae). “Slow” drivers like overfishing or nutrients can cause the system to flip from one state to another, but only after it’s soaked up a fair amount of abuse.
Feedbacks hold the systems in a stable state until a tipping point is reached. Once a coral reef flips to an algae-dominated state, those feedbacks prevent it from flipping back in the other direction. In other words, degraded systems are also resilient. Uh oh.
We see some depressing before and after photos of the Great Barrier Reef. Terry says that many scientists are skeptical about such anecdotal evidence. It sure gets the message across though.
Back to the science. As disturbances accumulate, it takes an ever-smaller extra disturbance to flip the system. High coral cover doesn’t necessarily mean the reef is resilient.
Example, the Jamaican coral reef. Terry shows some photos of a study site at 35m depth. Over several years the coral all but disappears. At that depth hurricane damage wasn’t an issue – instead it was more likely overfishing, nutrient inputs and climate change.
But there’s evidence that reefs can flip the other way. Taking action to “divert” sewage outflow or set up no take areas that protect herbivores, for example, can lead to positive changes.
Terry shows us one of his Australian experiments, pointing out how Australian parrot fish are “real ones”. He did an enclosure experiment and kept the fish out of a set of large cages. Sure enough the algae soon took over, but when he removed the cages it took only four weeks for those ’specially butch parrot fish to nibble it all back down again to square one.
Take home: we need to understand the dynamics of thresholds, and feedbacks.
Interventions must focus on all the slow drivers – looking at one in isolation won’t do any good. That kind of echoes the earlier stuff from the conference about how multiple impacts need to be studied together.
Similarly, measures of ecosystem status – such as coral cover – are of limited value on their own.
Next a lovely analogy about paddling down a river in a canoe. We know there’s a waterfall somewhere, and to protect the paddlers we need to know things like the current speed and distance to the waterfall. But what we’re doing at the moment is counting the number of people in the canoe! Stupid us. “When that number goes from two to zero, it’s too damn late”. Point made.
So what killed the Caribbean corals? The Diadema die-off in 1983 caused 99% to die in a ten-day period. There were roughly a million spiky urchins for every kilometer of coastline. Devastating. Following that the reef got choked up in green algae.
Since 1983 there has been little sign of a recovery, although they are coming back in some areas. Shallow areas are showing some signs of recovery, but there’s a long way to go. “Bring on Diadema!” Terry says. We should think about moving them around to get things moving quicker.
“There’s lots of bored tourists out there who might like to lend a hand.” Wouldn’t that be great?
Coral reef protect is a question of governance, Terry continues, moving into the final part of the talk. The area covered GBR MPA would be much harder to set up in the Caribbean, where more than ten island states could be involved.
Managing coral reefs isn’t just about ecology and biodiversity: there are also huge economic issues, such as food security for many parts of the world. We have to live in the real world – we can’t set the whole lot aside as a no-take area because people would starve.
Terry makes the point that there is also a flow of stuff from non-no-take areas into no-take areas, something all to often forgotten. Stuff like disease. Bad stuff. But also larvae too. The non-no-take areas tend to be much larger and more numerous, so their effect on NTAs shouldn’t be underestimated. Non-no-take areas need to be co-managed alongside NTAs. “We can’t just let the rest of the seascape go to Hell”.
Bombshell. The GBR is in just the kind of slowly degrading trouble that Terry’s been talking about. Ah, but then he puts up a slide about the recovery of Coral Trout stocks in NTAs within the Marine Park. We all know the study.
How to manage a coral reef for the future:
Scale up management efforts, learn from elsewhere.
Rezone with the aim of maintaining ecological function and resilience
Introduce new fishing regulations
Reduce nutrient and sediment run-off, improve water quality.
These approaches are forward-looking.
A fast-tracked paper has now appeared on PNAS online to coincide with this talk. Look it up! Click here to find it.
Finally, reefs are threatened but not doomed if we can avoid extreme climate change. That, run-off and overfishing have be sorted out. Local and global actions are needed. Prevention is better than cure. The planet won’t look like it did 100 years ago. We need to plan for the future.
Terry ends up with a message that we need to underline the notion that coral reefs aren’t doomed. Yay! Don’t write them off – it’s not too late to save them! TAKE THAT ONE HOME.
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